Predicting the Earth Pressure on Integral Bridge Abutments

Abstract

The soil adjacent to integral bridge abutments experiences daily and annual temperature-induced cyclic loading due to expansion and contraction of the bridge deck. This causes a particular soil response and complicated soil-structure interaction problem, with considerable uncertainties in design. This paper describes a method of calculating the effects of thermal cycling by using the results of laboratory cyclic stress path testing within a numerical model. Samples of stiff clay and sand were tested in the triaxial apparatus under stress paths typical for behind an integral abutment. Distinct behavior was observed for the two soils, with stiff clay showing relatively little buildup of lateral stress with cycles, whereas for sand stresses continued to increase, exceeding at-rest and approaching full passive pressures. To explore the implications of these findings on the soil-abutment interaction and to estimate the lateral stresses acting on the abutment as a whole, a numerical (finite difference) model was developed with a soil model reproducing the sand behavior at element level. The numerical model gave good agreement with published centrifuge and field data, and indicated that the stress profile specified in some current standards is conservative. Influence of abutment stiffness and wall friction is also quantified.